Cholesterol accumulation by macrophages impairs phagosome maturation.
Macrophages are key to the pathogenesis of atherosclerosis. They take up and store excessive amounts of cholesterol associated with modified low density lipoprotein, eventually becoming foam cells that display altered immune responsiveness. We studied the effects of cholesterol accumulation on phagosome formation and maturation, using lipid transport antagonists and cholesterol transport-deficient mutants. In macrophages treated with U18666A, a transport antagonist that prevents cholesterol exit from late endosomes/lysosomes, the early stages of maturation proceeded normally; phagosomes acquired Rab5, phosphatidylinositol 3-phosphate, and EEA1 and merged with LAMP-containing vesicles. However, fusion with lysosomes was impaired. Rab7, which is required for phagolysosome formation, was acquired by phagosomes but remained inactive. Maturation was also studied in fibroblasts from Niemann-Pick type C individuals that have defective cholesterol transport. Transfection of FcgammaIIA receptors was used to confer phagocytic capability to these fibroblasts. Niemann-Pick type C phagosomes failed to fuse with lysosomes, whereas wild type fibroblasts formed normal phagolysosomes. These findings indicate that cholesterol accumulation can have a detrimental effect on phagosome maturation by impairing the activation of Rab7, sequestering it and its effectors in cholesterol-enriched multilamellar compartments.
Huynh
Kassidy K
KK
Programme in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
Gershenzon
Elena
E
Grinstein
Sergio
S
D000736:Androstenes / Q000494:pharmacology; D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology; D050197:Atherosclerosis / Q000378:metabolism* / Q000473:pathology; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism / Q000648:ultrastructure; D005347:Fibroblasts / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D051907:Lysosomal Membrane Proteins / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism / Q000648:ultrastructure; D008264:Macrophages / Q000378:metabolism* / Q000648:ultrastructure; D008561:Membrane Fusion / Q000187:drug effects; D051379:Mice; D052556:Niemann-Pick Disease, Type C / Q000378:metabolism* / Q000473:pathology; D010588:Phagosomes / Q000378:metabolism* / Q000648:ultrastructure; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D017452:Receptors, IgG / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D020696:rab5 GTP-Binding Proteins; D000090802:rab7 GTP-Binding Proteins
D000736:Androstenes; D000924:Anticholesteremic Agents; C080568:Fc gamma receptor IIA; D051907:Lysosomal Membrane Proteins; D018129:Phosphatidylinositol Phosphates; D017452:Receptors, IgG; D033921:Vesicular Transport Proteins; C093846:early endosome antigen 1; D000090802:rab7 GTP-Binding Proteins; C000716463:rab7 GTP-binding proteins, human; C000716465:rab7 GTP-binding proteins, mouse; C006261:3-beta-(2-(diethylamino)ethoxy)androst-5-en-17-one; D002784:Cholesterol; D020691:rab GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins